Three-dimensional video camera and display systems available in the marketplace are based on capturing and presenting two viewpoints to the observer. Two cameras separated by a horizontal distance are focused and converged on a scene and the signal from each camera is presented to the appropriate eye. Methods for displaying stereoscopic video information include red/green anaglyphs, liquid crystal monitor shutter and passive glasses, liquid crystal shutter glasses and virtual reality head mounted displays. There exists a technique for displaying three-dimensional images without the need for glasses. The technique was developed through photography and is known as autostereoscopic technology. The concept for autostereoscopic technology is based on using a lenticular or barrier strip grating placed over the image in order to present a multitude of viewpoints to the observer. The lenticular and grating are designed to allow only narrow bands of information of the scene to be sent to the viewer's eyes from the display. If only two viewpoints are used, the viewer must keep a rigid head position in order to prevent seeing the opposite eye's views and thus a pseudoscopic or reverse relief condition. With four views the observer has greater latitude in head position and can see the shifting of objects with a corresponding head movement. This phenomenon is very useful in determining the spatial relationship of objects and is known as motion parallax.
Constructing an autostereoscopic display would require placing a lenticular or barrier strip over a display and presenting the proper image on the display. This procedure presents many difficulties based on the inherent characteristics of the displays. The cathode ray tube (CRT) is the preferred display in the marketplace based on its capability for size, refresh speed, color gamut and cost. A lenticular or barrier strip placed over a CRT has two significant problems. The first is that the linearity of the image on the display is not consistent from the center of the screen to the corners. A control system to ensure linearity would require a complex modification. The second problem is based on the thickness of the faceplate and the fact that it is physically impossible to resolve two adjacent viewpoints of information from a close (arm's length) viewing position. Flat panel displays are being developed that will overcome the linearity and faceplate issues. The flat panel display market consists of liquid crystal displays, electroluminescent displays, plasma displays and flat CRT's. The flat panel displays with the specifications needed for autostereoscopic use are not readily available in the marketplace and may only be in the future with a significant pricing level.
A stereoscopic video camera system consists of two cameras focused and converged on objects in the scene. The two cameras, however, must be perfectly matched in the areas of brightness and focus. Furthermore, a geometric distortion based on perspective is caused by converging or pointing two cameras toward the object and viewing the scene on a single monitor. Constructing a two camera system with zoom capability must have complex focus and convergence mechanisms.